A rotary circuit selection device generally uses a rotating shaft connected to a terminal to make or break a connection to one or more other terminals. In performing its function, a rotary switch also uses a detent mechanism. Merriam-Webster's Online Dictionary defines a detent as “a device (as a catch, dog, or spring-operated ball) for positioning and holding one mechanical part in relation to another so that the device can be released by force applied to one of the parts”. Basically, the detent aids a user of the switch in establishing and holding a knob position that equates to a desired electrical setting.
In order to set and hold a particular position, a detent often comprises a cam follower and a cam. The cam is generally an annular component with a hole in the middle. The surface of the cam that forms the hole is varied in contour. As a shaft is rotated a cam follower travels along the contour of the cam becoming seated and unseated in turn. Each seated position generally equates to a particular electrical setting while an unseated position is generally between circuits. This type of cam/cam follower configuration is particularly well illustrated in U.S. Pat. No. 6,617,534 issued to Goff et al. in September 2003. A problem with this type of detent, however, is that the size of the spring biasing the cam follower is dependent upon the size of the cam follower shaft. This is important because the amount of torque required to rotate the cam follower is related to the spring tension.
U.S. Pat. No. 4,059,738 issued to Mongeau in November of 1977 shows a another type of detent. The detent of the '738 patent has a cam follower that follows the outside contour of the cam rather than the inside contour. In any case, the cam has alternating raised and lowered portions that form seats for the cam follower. As with most detents, however, use of the switch causes both the cam and the cam follower to wear in a manner that causes play (i.e. movement when the cam follower is in a seated configuration) in the switch. Excessive play in the switch is undesirable because it can cause a circuit to be inadvertently opened or closed.
Thus, there is a need for methods and devices which can use higher tension springs and which do not become less accurate due to use.